Method for production of succinic acid and sulfuric acid by paired electrosynthesis

ABSTRACT

A method for the production of succinic acid and sulfuric acid by paired electrolytic synthesis is disclosed in the present invention. The method is described as following: in cathodic compartment of an electrochemical cell separated with cation exchange membrane, maleic acid or maleic anhydride is used as raw material, sulfuric acid as the cathodic reactant and the supporting electrolyte of the reaction system, succinic acid is thus synthesized by the electro-reduction reaction at cathode. In anodic compartment, the aqueous sulfuric acid solution containing iodide ion is used as electrolyte, iodide ion is anodized to form I 2  and I 3   − . SO 2  gas is fed into the circulated anolyte, reacting with I 2  and I 3   −  to form sulfuric acid and regenerate iodide ion. Simultaneously the evaporated hydroiodic acid and distilled water are returned to the anolyte circulation system. The cell voltage and the cost of production are reduced significantly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/CN2011/072346, with an international filing date of Mar. 31,2011, designating the United States, now pending, and further claimspriority benefits to Chinese Patent Application No. 201010137720.4,filed Apr. 1, 2010. The contents of all of the aforementionedapplications, including any intervening amendments thereto, areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for production of succinic acid andsulfuric acid by paired electrosynthesis.

2. Description of the Related Art

Succinic acid is an important chemical raw material which is colorlessor white crystalline, odorless and sour taste. It is widely used in thefields of pharmaceuticals, pesticides, fine chemicals and alkyd resin.In recent years, succinic acid has been widely used in the fields ofbiodegradable plastics, polybutylene succinate (PBS), and organiccoatings etc.

There are three main methods to synthesize succinic acid: chemicalsynthesis, biological conversion and electrolysis method.

At present, most of succinic acid for industrial use is produced bychemical synthesis method which includes oxidation and catalytichydrogenation. Although those technologies have been developed andapplied practically, there are still many problems existing such as theuncontrollable side reactions, low yield, low purity of the product,high requirement in operation and usage of expensive catalyst, etc.Furthermore, there is serious environmental pollution in its productionprocess.

In recent years, the method of producing succinic acid with bacterial ormicrobial fermentation has become a research focus worldwide because ituses starch, glucose, milk and other waste as raw material. However, alarge amount of research still needs to be investigated and completed,such as low extraction efficiency, low production and conversion rate,high production cost, generation of a large amount of wastewater, etc.It is estimated that more than 10 tons of wastewater is generated inproducing 1 ton of succinic acid. Therefore, it is hard to meet therequirement of industrial production. At present, the biologicalconversion technology is still limited to the laboratory scale and needsmuch more time to be commercialized.

Succinic acid can be also produced by electrolytic reduction method inwhich maleic acid or maleic anhydride is used as the reactant. Theproduction of succinic acid with electrolytic technology had beenindustrialized in 1930s. After nearly 80 years of development of thetechnology, the electrolytic synthesis technology becomes more and moremature, leading to accomplish higher conversion ratio, yield, purity andcurrent efficiency in producing succinic acid. In the meantime, zerodischarge of wastewater is reached by recycling mother liquor.Therefore, the electrolytic technology has been considered as a greenchemical synthesis technology.

According to the literature, the electrolytic technology of succinicacid production can be fulfilled in two ways named as membrane techniqueand membrane-free technique. At present, the membrane-free technique hasbeen adopted widely, as indicated in the patents 200710047530.1 (Chinesepatent application), 200610148269. x(Chinese patent application), etc.The electrooxidation reaction with oxygen evolution has almost alwaysbeen adopted as the anodic reaction in most present industrialproduction of succinic acid in which PbO₂ anode is chosen as anodematerial. However, the disadvantage in this method is that the cellvoltage is high, the life of PbO₂ anode is short and the initialinvestment of the anode is high. Other than oxygen evolution reaction,it was also reported that the electro-oxidation reaction of glyoxal toglyoxylic acid had been adopted as the anodic reaction (Fine Chemicals,Chinese journal, 1997, 14(5), 56˜57), but the yields of glyoxylic acidand succinic acid are both relatively low.

In the present invention, a new technology for electrolytic synthesis ofsuccinic acid and sulfuric acid is disclosed. The principle of thetechnology is based on the paired electrolytic synthesis, in whichsuccinic acid is formed by the electro-reduction of maleic acid (ormaleic anhydride) and the redox couple of I⁻/I₂ is used as anodicmediator to produce sulfuric acid. Sulfuric acid is obtained in theanolyte circulation system through the redox reaction of I₂ (or I₃ ⁻)with sulfur dioxide gas fed into the anolyte from outside. Iodine (or I₃⁻) is generated through the electrooxidation reaction of iodide.Therefore, the present invention is a novel technology in producingsuccinic acid and sulphuric acid at the same time with pairedelectrolytic technology.

SUMMARY OF THE INVENTION

The present invention discloses a technical solution for producingsuccinic acid and sulfuric acid with paired electrolytic synthesis. Byselecting suitable anodic reaction, the cell voltage and the cost ofproduction are reduced significantly, the current efficiency is high andthe electrolyte is recycled. Meantime, the problems of short lifetime ofanode and environmental pollution are solved.

In order to solve the above technique problems, a technical solutionadopted in the present invention is as following.

A technical solution in producing succinic acid and sulfuric acid withpaired electrolytic synthesis, said solution is: using maleic acid ormaleic anhydride as raw material of the cathodic reaction, sulfuric acidas the cathodic reactant and the supporting electrolyte of the reactionsystem; the anolyte and cathloyte compartments in the electrochemicalcell are separated each other with cation-exchange membrane; thereaction occurred on the cathode is described as the followingequations:

As the electrolytic reaction in the cathodic compartment proceeds to acertain degree, succinic acid is generated by post-processing catholyte.The technicians in this field can monitor the extent of the reactionaccording to the electricity consumed theoretically.

In the anodic compartment, sulfuric acid solution containing iodide ionis used as anolyte, iodide ion is anodized to form I₂ and I₃ ⁻, and SO₂gas is fed into the anolyte continuously which is circulated within thesystem. Sulfuric acid is produced and iodide ion is regenerated throughthe redox reaction of I₂ and I₃ ⁻, with sulfur dioxide. When theconcentration of sulfuric acid in the anolyte reaches a certain degree,the anolyte is post-processed to obtain higher concentration sulfuricacid. Simultaneously, evaporated hydroiodic acid and the distilled waterare isolated and returned to the anolyte circulation system.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of accompanying drawings will be provided below.

FIG. 1 is a schematic diagram of an experimental apparatus applied inthe current invention embodiment, where: 1-anode, 2-cathode, 3-anolytetank, 4-catholyte tank, 5-cation exchange membrane, 6-flow controllingvalve, 7-electrolyte circulation pump, 8-SO₂ inlet.

FIG. 2 is the process flow diagram of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Detailed description will be given below in conjunction withaccompanying drawings.

In anodic compartment, the aqueous sulfuric acid solution containingiodide ion is used as the electrolyte and the sulfur dioxide gas is fedinto the anolyte circulation system, the following electrooxidationreaction takes place.

2I⁻→I₂+2e (or 3I⁻→I₃ ⁻→2e)  (1)

In the above anodic reaction, the iodide ion is regenerated through thefollowing chemical redox reaction of I₂ and I₃ ⁻ with SO₂ or H₂SO₃. Inthe meantime, sulfuric acid is produced as well. The reactions can beexpressed as the followings.

I₂+SO₂+2H₂O═H₂SO₄+2HI  (2)

H₂SO₃+I₂+H₂O=4H⁺+2I⁻+SO₄ ²⁻  (3)

I₃ ⁻+SO₂+2H₂O=4H⁺+3I⁻+SO₄ ²⁻  (4)

In the anodic compartment, sulphur dioxide gas is fed into the anolytewhere sulfurous acid is formed through the reaction of SO₂ and water.

A cation exchange membrane is used to separate the electrochemical celladopted in the present invention. In said electrochemical cell, theanode materials resistant to the corrosion in strongly acidic solutioncontaining iodide are used as the anode, as preferred, graphite and DSAelectrode (RuO₂—TiO₂/Ti anode). The cathode materials with highoverpotential of hydrogen evolution are employed as cathode, aspreferred, lead and lead alloys. The distance between the cathode andanode is kept as short as possible, as preferred, 5˜50 mm.

In the reaction process of the present invention, the preferredconditions are: the concentration of reactants in the cathodiccompartment is controlled as following: sulfuric acid 0.5˜3 mol/L,maleic acid 0.5˜3 mol/L; the concentration of reactants in the anolyteis controlled as following: sulfuric acid 0.5˜7 mol/L, iodide ion 0.5˜4mol/L. The molar ratio of the total of I₂ and I₃ ⁻, generated throughthe anodic reaction to SO₂ fed from the outside is controlled at1:(1˜1.5). The preferred current density of the cathode and anode is300˜1200 A/m² and 300˜1500 A/m², respectively.

The electrolysis process of the present invention is operated usingbatch-type and continuous-type modes. Said continuous-type mode iscarried out as following: adding reactants needed continuously, takingpart of electrolyte out of the system for post-processing after theelectrolysis reaction reaches a certain degree, returning the motherliquor from the post-processing to the electrolyte system aftersupplementing raw material; said batch-type mode is operated as follows:adding catholyte in one time or several times, feeding SO₂ to theanolyte continuously, replacing the electrolyte with fresh electrolytewhen the electrolysis reaction reaches a certain degree, post-processingthe electrolyte containing reaction products, supplementing raw materialin the post-processed electrolyte and using it as fresh electrolyte.

The post-processing method of the catholyte in the present invention isas following: cooling the catholyte, filtering the cooled catholyte toget succinic acid crystal, rinsing the succinic acid crystal and dryingit to obtain succinic acid product. The mother liquor generated infiltering is returned to the catholyte circulation system aftersupplementing maleic acid or maleic anhydride. As a result, the yield ofsuccinic acid is increased, the consumption of raw material is reduced,and the cost of production is decreased. In the meantime, greenproduction is achieved.

The post-processing method of the anolyte in the present invention is asfollowing: post-processing the anolyte to get concentrated sulfuric acidafter the concentration of sulfuric acid reaches a certain degree, inthe meantime, returning the evaporated hydroiodic acid and steam to theanolyte circulation system.

In addition, the temperature of the electrolyte has a large influence onthe electrolysis reaction because the solubility of succinic acidincreases with the temperature of the electrolyte. When the temperatureof the electrolyte is too low, large amount of succinic acid willprecipitate to form crystal during the process of electrolysis, leadingto the increase of the cell voltage and affecting the electrolysisreaction. However, high temperature of the electrolyte will damage theequipment of electrolysis and shorten the life of membrane. The reactiontemperature is maintained at 20˜70° C., as preferred, 30˜50° C.

The experimental equipment used in the present invention includes: acation membrane-separated electrochemical cell, an anolyte tank and ancatholyte tank. Said electrochemical cell is separated into anodiccompartment installed with anode and cathodic compartment installed withcathode. Said electrochemical cell could be assembled and connected inmono-polar or bi-polar way. The inlet port of said anodic compartment isset at the bottom and connected to the outlet port of the anolyte tankthrough pump and flow controlling valve. The outlet of said anodiccompartment is set at the top and connected to the inlet port of theanolyte tank, constituting an anolyte circulation system. The inlet portof said cathodic compartment is set at the bottom and connected to theoutlet port of the catholyte tank at the bottom through pump and flowcontrolling valve. The outlet of cathodic compartment is set at the topand connected to the inlet port of catholyte tank, constituting acatholyte circulation system. In the present invention, there are twoways for sulfur dioxide gas to be fed into the anolyte circulationsystem: one is to feed sulfur dioxide gas into the anodic compartmentdirectly where an oxidation-reduction reaction takes place, the other isto feed sulfur dioxide gas into the anolyte tank where theoxidation-reduction reaction takes place.

Compared with the related art, the beneficial results of the presentinvention include: (1) reducing the energy consumption of succinic acidelectrolytic synthesis significantly by adopting appropriate pairedanodic and cathodic reactions, (2) decreasing the initial investment andproduction cost by using inexpensive anode material, overcoming theproblem of short lifetime of anode, (3) providing a new wet technologyto produce sulfuric acid at low temperatures, (4) increasing currentefficiency, recycling electrolyte and achieving green production. Thetechnology of the present invention is suitable for industrial scaleproduction.

Example 1

A mono-polar membrane-separated electrochemical cell is used. Graphiteand lead are used as anode and cathode, respectively. The apparent areaof both the anode and the cathode is 50 cm². The distance between theanode and the cathode is 40 mm. A homogeneous cation exchange membranemade of polyvinylidene fluoride (F101 type) is used in the cell.

The electrolytic technological parameters are chosen as follows: theinitial concentration of KI and sulfuric acid in the anodic compartmentis 1 mol/L, the initial concentration of sulfuric acid and maleicanhydride in the cathodic compartment is 1 mol/L, the temperature of theelectrolyte is controlled at the range of 30˜35° C. The electrolyte inthe anolyte and cathodic compartments is circulated through pump set ontheir respective tank. The total amount of anolyte and catholyte is 3liters, respectively. SO₂ gas is fed into the anodic compartment. Slightexcess of SO₂ gas is kept to ensure that the solution in the anodiccompartment remains green yellow (not brown). The current density of theelectrolysis reaction is 1000 A/m², and the average cell voltage is 2.38V.

After 10 hours at constant current density, the electrolysis reaction isstopped, and the catholyte is taken out for post-processing. Afterpost-treatment which includes cooling, crystallization, filtration,rinsing with icy deionized water and drying, 68.4 g succinic acid isobtained finally. The cathodic current efficiency is calculated to be95.1%.

Example 2

A mono-polar membrane-separated electrochemical cell is used. Graphiteand lead are used as anode and cathode, respectively. The apparent areaof both the anode and the cathode is 50 cm². The distance between theanode and the cathode is 40 mm. A homogeneous cation exchange membranemade of polyvinylidene fluoride (F101 type) is used in the cell.

The electrolytic technological parameters are chosen as follows: theanolyte in the anodic compartment is the anolyte after electrolysisreaction in Example 1, the catholyte in the cathodic compartment is themother liquor of the catholyte in Example 1. The initial concentrationof maleic acid in the catholyte is adjusted to be 1 mol/L bysupplementing maleic anhydride. The temperature of the electrolyte iscontrolled at the range of 50˜55° C. Other technological parameters arethe same as those in Example 1. The average cell voltage is 2.26 V.

After 5 hours at constant current density, the electrolysis reaction isstopped, and the catholyte is taken out for post-processing. Afterpost-treatment which includes cooling, crystallization, filtration,rinsing with icy deionized water and drying, 51.1 g succinic acid isobtained finally. The cathodic current efficiency is calculated to be94.2%.

Example 3

A mono-polar membrane-separated electrochemical cell is used. DSA andlead are used as anode and cathode, respectively. The apparent area ofboth the anode and the cathode is 50 cm². The distance between the anodeand the cathode is 20 mm. A homogeneous cation exchange membrane made ofNafion 117 is used in the cell.

The electrolytic technological parameters are chosen as follows: theanolyte in the anodic compartment is the anolyte after electrolysisreaction in Example 2, the catholyte in the cathodic compartment is themother liquor of the catholyte in Example 2. The initial concentrationof maleic acid in the catholyte is adjusted to be 1.2 mol/L bysupplementing maleic anhydride. The temperature of the electrolyte iscontrolled at the range of 30˜35° C. SO₂ gas is fed into the anolytetank. Other technological parameters are the same as those in Example 1.The average cell voltage is 1.38 V.

After 10 hours at constant current density, the electrolysis reaction isstopped, and the catholyte is taken out for post-processing. Afterpost-treatment which includes cooling, crystallization, filtration,rinsing with icy deionized water and drying, 52.2 g succinic acid isobtained finally. The cathodic current efficiency is calculated to be94.9%.

Example 4

A mono-polar membrane-separated electrochemical cell is used. Graphiteand lead are used as anode and cathode, respectively. The apparent areaof both the anode and the cathode is 100 cm². The distance between theanode and the cathode is 15 mm. A homogeneous cation exchange membranemade of Nafion 117 is used in the cell.

The electrolytic technological parameters are chosen as follows: theanolyte in the anodic compartment is the anolyte after electrolysisreaction in Example 3, the catholyte in the cathodic compartment is themother liquor of the catholyte in Example 3. The initial concentrationof maleic acid in the catholyte is adjusted to be 0.8 mol/L bysupplementing maleic acid. The temperature of the electrolyte iscontrolled at the range of 40˜45° C. SO₂ gas is fed into the anodiccompartment. The current density of the anode and the cathode iscontrolled at 750 A/m². Other technological parameters are the same asthose in Example 1. The average cell voltage is 1.59V.

After 2 hours at constant current density, the electrolysis reaction isstopped, and the catholyte is taken out for post-processing. Afterpost-treatment which includes cooling, crystallization, filtration,rinsing with icy deionized water and drying, 31.2 g succinic acid isobtained finally. The cathodic current efficiency is calculated to be94.5%.

Example 5

A mono-polar membrane-separated electrochemical cell is used. Graphiteand lead are used as anode and cathode, respectively. The apparent areaof both the anode and the cathode is 100 cm². The distance between theanode and the cathode is 15 mm. A homogeneous cation exchange membranemade of Nafion 117 is used in the cell.

The electrolytic technological parameters are chosen as follows: theanolyte in the anodic compartment is the anolyte after electrolysisreaction in Example 4, the catholyte in the cathodic compartment is themother liquor of catholyte in Example 4. The initial concentration ofmaleic acid in the catholyte is adjusted to be 0.8 mol/L bysupplementing maleic acid. The temperature of the electrolyte iscontrolled at the range of 50˜55° C. SO₂ gas is fed into the anodiccompartment. The current density of the anode and the cathode iscontrolled at 1200 A/m². Other technological parameters are the same asthose in Example 1. The average cell voltage is 1.64V.

After 2 hours at constant current density, the electrolysis reaction isstopped, and the catholyte is taken out for post-processing. Afterpost-treatment which includes cooling, crystallization, filtration,rinsing with icy deionized water and drying, 49.7 g succinic acid isobtained finally. The cathodic current efficiency is calculated to be94.1%.

After the above five examples (from Example 1 to Example 5) arefinished, the anolyte is taken out for analysis. The results show theconcentration of sulfate in the anolyte is 1.83 mol/L, the total averageanodic current efficiency is calculated to be 96.56%. The anolyte istaken out to be concentrated. After the volume of the anolyte is reducedto 1 L by evaporating, the concentration of sulfuric acid is found to be5.49 mol/L. The evaporated substances are collected and returned to theanolyte circulation system after cooling.

The invention claimed is:
 1. A method for the production of succinicacid and sulfuric acid by paired electrolytic synthesis comprising:inside cathodic compartment of an electrochemical cell separated withcation exchange membrane, maleic acid or maleic anhydride is used as rawmaterial, sulfuric acid as the cathodic reactant and the supportingelectrolyte of the reaction system, succinic acid is thus synthesized bythe electro-reduction reaction at cathode. When the extent ofelectrolysis reaction reaches a certain degree, catholyte is taken outand post-processed to obtain succinic acid. In anodic compartment, theaqueous sulfuric acid solution containing iodide ion is used aselectrolyte, iodide ion is anodized to form I₂ and I₃ ⁻. SO₂ gas is fedinto the circulated anolyte, reacting with I₂ and I₃ ⁻ through redoxreaction to form sulfuric acid and regenerate iodide ion in anolyte.When the concentration of sulfuric acid in the anolyte reaches a certaindegree, the anolyte is taken out to be concentrated to obtain sulfuricacid of high concentration. Simultaneously, the hydroiodic acid and thedistilled water evaporated from the anolyte are returned to the anolytecirculation system.
 2. The method of claim 1, wherein inside saidelectrochemical cell, graphite or titanium-supported RuO₂—TiO₂ electrodeis used as anode, lead or lead alloys as cathode. The distance betweenthe cathode and the anode is 5˜50 mm.
 3. The method of claim 1, whereinduring the process of electrolysis reaction, the concentration ofreactants in said catholyte is controlled as following: sulfuric acid0.5˜3 mol/L, maleic acid 0.5˜3 mol/L; the concentration of reactants insaid anolyte as following: sulfuric acid 0.5˜7 mol/L, iodide ion 0.5˜4mol/L. The molar ratio of the total amount of I₂ and I₃ ⁻ generatedthrough the anodic reaction to SO₂ fed from outside is controlled at1:(1˜1.5).
 4. The method of claim 3, wherein the current density ofcathode and anode is controlled at 300˜1200 A/m² and 300˜1500 A/m²,respectively.
 5. The method of claim 1, wherein the post-processing ofsaid catholyte after electrolysis reaction comprising: said catholytethus obtained is cooled, precipitated, filtered, rinsed, dried to obtainsuccinic acid; the mother liquor from filtration is returned to saidcathodic compartment after supplementing maleic acid or maleicanhydride.
 6. The method of claim 1, wherein the temperature of saidelectrolysis reaction is controlled at the range of 20-70° C.
 7. Themethod of claim 1, wherein the temperature of said electrolysis reactionis controlled at the range of 30-50° C.
 8. The method of claim 1,wherein said paired electrolytic synthesis is operated in two modes:batch-type and continuous-type.